The invention relates to a method of executing a measurement or control action and to a controller for carrying out the method. The invention also relates to a method for synchronizing several measurement and/or control actions.
The term measurement action is to be understood as a process where data are acquired with a measuring device, as well as stored or transmitted onward. The term control action is to be understood more generally as a process, by which a technical device is caused to perform any action, e.g., a movement, an electrical switching process, etc.
Such measurement or control action includes typically a sequence of individual switching processes, for example switching an operating voltage on, activating or deactivating a measuring channel, reading from or writing to a memory register, causing a data transfer, and the like.
A device which initiates or causes a measurement or control action of a technical device (in particular a measuring device) is referred to as controller.
Two actions are referred to as being synchronous if the sequence of operations of both actions is determined by the same time scale. However, in the context of the above definition, two synchronous actions need not necessarily be executed simultaneously. It is only important that a defined and determinable time correlation exists between each instant of the first action and each instant of the second action.
It is often necessary in practical applications to perform an action at a certain, precisely determined time or to at least know the exact time when an action is performed. This requirement applies in particular if the timed operation of several devices, in particular widely spaced devices, is coordinated within narrow times. Seismographic measurement methods are one example of such system.
In such method, the propagation of a shock or pressure wave in the ground is typically recorded by a number of spatially distributed seismic sensors. The location of a seismic source can be localized (e.g., earthquake detection) by comparing the seismic pattern recorded by the different sensors, or conclusions can be drawn about the structure of the ground by producing an artificial seismic event (seismographic ground measurements). The significance of the results from such investigation depends considerably on the temporal precision with which the seismic patterns from different sensors can be correlated. The measurement actions executed by different sensors must therefore be precisely synchronized.
Similar requirements for synchronizing measurement actions also apply to acoustic measurement methods (sonar, etc.) and to measurements of the oscillation characteristic of a mechanical system.
Typically, a measurement or control action is “triggered” by a clock, i.e., initiated at a certain instant. If different actions are triggered by independent clocks, then these actions are synchronous only to a limited extent due to the time differences caused by the inaccuracy of the clocks. The synchronism can be improved by aligning their clocks, for example, by Global Positioning Satellite (GPS) signals or radio timing signals.
A timing inaccuracy and an accompanying loss in synchronism may also result from the fact that a measurement or control action is typically not a process performed at an exact instant, but a process that occurs over a certain time interval due to the potentially large number of required switching processes. The actual measurement or control is therefore not executed at the exact time when a trigger command is outputted, but at a later time which has a comparatively poor temporal correlation with the trigger time.